Polycarbonate has found many uses because, in general, it combines a high level of heat resistance and dimensional stability with good insulating and non-corrosive properties, and it is easily molded. It does, however, suffer from a tendency to craze and crack under the effects of environmental stress, especially contact with organic solvents such as gasoline. Polycarbonate which has crazed is, undesirably, more likely to experience brittle rather than ductile failure. This disadvantage has been somewhat relieved by the practice of blending polycarbonate with substances such as various olefin polymers. These added substances are capable of improving the resistance of polycarbonate to solvents, but they tend to delaminate and cause an offsetting reduction in the toughness, impact resistance and weldline strength of the blended high gloss polycarbonate composition. It would accordingly be desirable if substances admixed with polycarbonate for the purpose of improving its resistance to organic solvents and other environmental stresses did not also deleteriously affect its toughness and impact and weldline strength, and cause delamination as evidenced by peeling or splintering.
In Chung, U.S. Pat. No. 4,554, 315, a system to promote the level of mechanical properties of polycarbonate is described wherein polycarbonate is blended with a polyester, an epoxide-containing modifier (preferably containing styrene and methyl methacrylate), and 5-30 percent of a core-shell, impact modifiying graft polymer. However, no recognition exists therein of the possibility of strengthening polycarbonate while maintaining a useful level of solvent resistance by employing a graft polymer in the system at levels below 5 percent, or by employing none at all, or by employing in place of the graft polymer a thermoplastic elastomer or a rubber-modified sytrene/acrylonitrile copolymer.
In Japanese Patent Publication No. 62-184,051 (1987), compositions are described containing polyester, polycarbonate, a butadiene-based graft copolymer, an ethylenic copolymer and an epoxy-containing modifier. All five of these components are said to be necessary to achieve an acceptable level of impact strength and aesthetics in a molded part. However, no recognition exists therein of the possibility of improving the impact strength of a molded part even further by omitting the ethylenic copolymer from such a composition and by, optionally, also omitting the butadiene-based graft copolymer therefrom, in favor of a thermoplastic elastomer.